Shooting Blue Screen: The Adkins WayThere’s no turning back. Shooting against a colored screen—green or blue—is here to stay. This is especially true in the HD world, where such shots are becoming increasingly common as more and more films use virtual reality as a backdrop.Creating a convincing composite image with this technology often depends on the quality of the foreground image against a blue or green screen. Case in point is Sky Captain and the World of Tomorrow, which shot all its actors in the studio against a colored screen and then keyed them over backgrounds in post.For Sky Captain cinematographer Eric Adkins, shooting a blue or green screen is half art and half science. Here he offers some tips of the trade.Adkins studied at Cal Arts with Sky Captain director Kerry Conran, and shot the six-minute demo Conran used to sell the project. Before his work on the full-length film he shot various jobs with a high digital composite quotient.“I was the stop-motion unit DP for Mars Attacks! when they were working with puppets on blue screen, before they decided to go digital CGI,” says Adkins. He also spent time as DP for the TV series The PJs, which used stop motion and incorporated blue- and green-screen elements.When he was brought on board for Sky Captain, he took on more than what was expected from most DPs. So he started 10 months prior to the actual shoot and worked closely with visual effects supervisor Darin Hollings on pre-production. And even though the budget expanded with the addition of high-profile actors, the original five-and-a-half week schedule to shoot the principle actors never changed.Adkins made several tests to choose the best color screen to use behind the actors. “We experimented with both blue and green screens and the blue faired better than the green,” he says. “When you’re staring at a green screen week after week, it can become annoying. Every time you turn your head away you start to see pink. Your eye is used to larger amounts of blue, such as a blue sky, so you’re not optically offended by it.”Adkins also shot normal, overexposed, and underexposed test images. “The overexposed green-screen images looked yellow. We found the blue screen gave us an overall better range of lighting options.” In addition, Adkins had actress Gwyneth Paltrow’s blonde hair to work with, which keyed better in motion-blur tests against blue than green.Choosing blue over green screen meant making certain adjustments in the camera. According to Adkins, the blue channel in the Sony HDW-F900 camera is the last prism in the camera block. “The image goes through all that glass to get to the blue chip. So they amp up the blue in the camera [and push it electronically] to try to match red and green, which are brighter.“To help compensate for the lower light level in the blue channel, I shot everything at -3dB [gain level],” Adkins adds. “If you turn the gain up when you shoot, as you might for the television show Cops, you make the camera more sensitive to light. Turning down the gain to -3dB cleaned up the grain [noise] to a point where we gained a finer grain around the overall picture, which also helped the edges when compositing. It also meant that we lost some of the light [coming into the lens].”Adkins also turned off the color matrixes in the camera and edge detail to shoot as raw as possible. And to help give him a 1930s film noir look, he shot through a polarizing filter, which meant he lost almost two stops of light, in addition to the 2/3 of a stop he lost because of shooting at -3dB. Adkins adds, “Shooting with a polarizing filter helped soften the nasty glare and helped control highlights.”Adkins adds a bit of advice for DPs who are entering this new world of virtual filmmaking. “Don’t be shy about stepping up and taking on the additional responsibilities that may not be part of your normal job range. It may not always seem like a natural overlap, but to make a film work out you may have to make a hybrid of yourself.”
Written by Diana Weynand
